1. Field of Invention
This invention relates to a preformed step for use in a manhole and more particularly to such a step which includes a specially designed surface for retaining the step in a side of a manhole shaft.
2. Description of the Prior Art
The prior art includes a number of steps intended for use in manholes. Such a step is described in U.S. Pat. No. 4,100,997 to Peacock which includes a pair of free ends having a plurality of circular rings which are tapered and deformable and are operable to retain the step in place in the wall of a manhole shaft. Such rings, while operable for their intended use, increase the production cost of the step and may, after a period of time become relaxed thus allowing the step to loosen, causing a safety hazard to a person using the step. Additionally, such rings provide for relatively small surface area which is in contact with the shaft. Use of such rings for manhole steps are disclosed in German Patent No. 2,254,550, in U.S. Pat. No. 4,195,709 to Gianotti et al., and in U.S. Pat. No. 3,374,859 to Dobert.
An object of the instant invention is to provide an improved step which would be more securely retained in a side wall of a manhole shaft.
Another object of the instant invention is to provide a step having an increased surface area which will be operable to hold the step in a side wall of a manhole shaft.
Yet another object of the instant invention is to provide a step which will remain in place over an extended period of time.
Still another object of the instant invention is to provide a step which is usable with or without a socket molded in a manhole shaft.
Another object of the instant invention is to provide a manhole step assembly which is usable with both wet mix and dry mix concrete and will remain in place with either type of mix.
Another object of the instant invention is to provide a step assembly which will be inexpensive and easy to manufacture, and which will be durable in its intended environment.